I: Energy in Cells: An Overview II: Cellular Respiration (Gylcolysis, Kreb’s

Cycle, Electron Transport), and Fermentation

Nestor T. Hilvano, M.D., M.P.H.(Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain,

Textbook, 2012.)

Learning Objectives1. Discuss the transformation of energy.2. Describe metabolism, anabolic and catabolic

feactions.3. Explain how redox reactions are involved in

energy exchanges.4. Compare the reactants, products and energy yield

of the 3 stages of cellular respiration (glycolysis, kreb’s cycle, & electron transport).

5. Explain the role of electron transport chain in cellular respiration.

6. Describe fermentation of lactic acid and alcohol.7. Explain how the human body uses energy.

Overview

• 1st Law of Thermodynamics:• Potential (stored) energy is

neither created or destroyed• It can be transferred and

transformed to other forms (chemical, electrical, mechanical, light, or heat).

• Cells transform energy to perform work

• ATP is the primary energy currency of cells

Potential Energy in Food Is Converted to Kinetic Energy in a Hummingbird’s Body

Metabolism • Sum of all chemical reactions• ____ reaction is the process of building of complex (large) molecules from

simple molecules; requires energy (endergonic)• ____ reaction is the process of breaking down complex molecules into

simple molecules; releases energy (exergonic) a. Catabolic b. Anabolic c. oxidation d. reduction

• Energy is usually liberated from the ATP molecule to do work in the cell by a reaction that removes one of the phosphate-oxygen groups, leaving adenosine diphosphate (ADP). When the ATP converts to ADP, the ATP is said to be spent. Then the ADP is usually immediately recycled in the mitochondria where it is recharged and comes out again as ATP

Figure 5.12A_s2

ADP: Adenosine Diphosphate

P P P Energy

H2OHydrolysis

Ribose

AdenineP P P

Phosphategroup

ATP: Adenosine Triphosphate

• Energy transfer/transformation increases entropy (measure of disorder/degree of randomness)

• Living cells maintain order through continual input of energy.

Redox Reactions• Redox reactions - transfer of electrons (negative

charge) during chemical reactions, releases energy stored in organic molecules

• Oxidation - loss of electrons (LEO)• Reduction - gain of electrons (GER)

Figure 6.5A

Glucose Heat

C6H12O6 O2 CO2 H2O ATP6 6 6

Loss of hydrogen atoms(becomes oxidized)

Gain of hydrogen atoms(becomes reduced)

p. 91

The transfer of H to O , make water (reduced) and yield energy (ATP)

Enzymes are often arranged in the cell in ways that facilitate the orderly series of chemical reactions

Figure 6.5C

Controlledrelease ofenergy forsynthesisof ATP

NADH

NAD

H

H O2

H2O

2

2

2

ATP

Electron transport chain

21

• In cellular respiration, electrons fall down an energy staircase and finally reduce O2.

Other carriers of Electrons

• NAD (Nicotinamide Adenine Dinucleotide)- NAD+ (oxidized); NADH + H (reduced)

• NADPH (Nicotinamide Adenine Dinucleotide Phosphate• FAD (Flavin Adenine Dinucleotide)

Uses of ATP (energy) 1. Mechanical Work= ___

2. Transport work= ___

3. Conduction of impulses= ___

4. Chemical Work= ___

a. Generate electricity in nerve

b. Movement (muscle contraction) or locomotion

c. Biosynthesis of complex molecules during active growth, repair, and replaced damaged molecules

d. Active transport of solute across cell membrane

Fig. 9-2

Lightenergy

ECOSYSTEM

Photosynthesis in chloroplasts

CO2 + H2O

Cellular respirationin mitochondria

Organicmolecules+ O2

ATP powers most cellular work

Heatenergy

ATP

Harvesting Chemical Energy

Cellular Respiration• Process of harvesting energy from glucose to

generate ATP.• 3 stages:

1. Glycolysis2. Citric Acid (krebs) Cycle3. Oxidative Phosphorylation (electron transport

& chemiosmosis)

• Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration; powered by redox reactions

• A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

Glycolysis• Occur in the cytoplasm. • Does not require oxygen• Breakdown of glucose into 2 molecules of

______, and produces a net of ____ ATP and _____ NADH

Formation of Acetyl CoA• In the presence of O2, pyruvate enter the

mitochondia • Before the krebs cycle can begin, 2 Pyruvates are

converted into 2 AcetylCoA (C2)• Produced 2 AcetylCoA and 2 NADH

Krebs (Citric Acid) Cycle• Occurs in mitochondrial matrix; requires

oxygen

• Acetyl CoA enters the Krebs cycle

• Joins a 4 carbon molecule to produce citrate (C6)

• Cycle twice to produced 4 Co2, 2 FADH2, 6 NADH, and 2 ATP

Oxidative Phosphorylation• Final stage of cellular respiration; occurs in

mitochondrial membrane (eukaryotes) or plasma membrane (prokaryotes)

• Involves Electron Transport Chain and Chemiosmosis

• NADH and FADH2 (energy carriers) shuttle electrons through the ETC to O2, final electron acceptor; and form H2O, as waste product.

• ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP; this is chemiosmosis, the use of energy in a H+ gradient to drive cellular work

• Produce 34 ATP

Fig. 9-16

Protein complexof electroncarriers

H+

H+H+

Cyt c

Q

V

FADH2 FAD

NAD+NADH

(carrying electronsfrom food)

Electron transport chain

2 H+ + 1/2O2H2O

ADP + P i

Chemiosmosis

Oxidative phosphorylation

H+

H+

ATP synthase

ATP

21

Cellular Respiration

In summary:

gylcolysis - 2 ATP

Kreb’s Cycle - 2 ATP

Oxidative Phosphorylation - 34 ATP

Total ----------------------------- 38 ATP

Fermentation

• Occurs in the ________ of oxygen (anaerobic); uses phosphorylation to generate ATP

• Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis

• Two common types are ______fermentation and ______ fermentation

• Alcohol fermentation by yeast, release CO2 gas

Fig. 9-18a

2 ADP + 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 NADH2 NAD+

+ 2 H+CO2

2 Acetaldehyde2 Ethanol

(a) Alcohol fermentation

2

Final electron acceptor

Fermentation

• In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2

• Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt

• Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

Fig. 9-18b

Glucose

2 ADP + 2 P i 2 ATP

Glycolysis

2 NAD+ 2 NADH+ 2 H+

2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

Final electron acceptor

Compare Cellular (Aerobic) Respiration and Fermentation (Anaerobic)

• Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate

• The processes have different final electron acceptors: O2 in cellular respiration and an organic molecule (such as pyruvate or acetaldehyde) in fermentation

• Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

• Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2

• Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration

Homework 1. Define terms: Metabolism, catabolism, anabolism, aerobic

(cellular) respiration, fermentation, oxidation, reduction, glycolysis, chemiosmosis,

2. Describe briefly the 3 stages of cellular respirations (glycolysis, kreb cycle, and oxidative phosphorylation) noting its reactants and final products.

3. Discuss at least 3 ways how we use energy (ATP) for cellular functions.

4. Describe the 2 types of fermentation.

5. Distinguish between obligate and facultative anaerobes.

6. What are the electron carriers (donors) in electron transport?

7. What is the final electron acceptor and waste product in cellular respiration?

8. What intermediate molecule is needed to proceed to Kreb’s cycle?